/Engine/Source/Runtime/Engine/Public/BonePose.h
The tricky bit is that SkelControls deliver their transforms in Component Space, But the blending is done in Local Space. Also we need to refresh any Children they have that has been previously converted to Component Space.
void LocalBlendCSBoneTransforms ( const [TArray](API\Runtime\Core\Containers\TArray)< struct [FBoneTransform](API\Runtime\Engine\FBoneTransform) > & BoneTransforms, float Alpha )